In this proposal I describe a model system for the experimental analysis of the regulation of gene expression during the development of a complex eukaryote. The catalase gene-enzyme system of maize is well suited for studying the control of gene expression in an eukaryote in that, as we have already established, it is comprised of at least two distinct genes which are differentially expressed during maize development and synthesize their respective products at different rates. Expression of the CAT genes appears to also be affected by changing patterns of subcellular compartmentation, and by an endogenous proteinaceous catalase-specific inhibitor. The system responds to external signals and its developmental program can be perturbed by varying light phases and by hormones. The proposed research will be directed at further elucidating the molecular and genetic mechanisms which underly the differential expression of the CAT genes both temporally and spatialy. Some focal points of the proposed research are, (1) further purfication and characterization of the specific inhibitor and its role in regulating catalase expression, (2) isolation and characterization of mutants affecting the temporal, tissue-specific, and high and low intensity expression of the enzyme and the inhibitor, (3) to locate the CAT genes on maize chromosomes, and (4) to determine underlying mechanisms for the apparent catalase tissue-specific differences. Further analysis of the intracellular compartmentation of catalase might help clarify the processing mechanism(s) and may give clues as to the physiological role(s) of the enzyme and the need for multiple forms.